The present invention relates to a vehicular navigation system which retrieves coordinate points of road configurations included in road map data stored in a memory device, determines road curves and informs the determined road curves.
JP-A-9-189565 discloses a conventional vehicular navigation system. This system uses three successive coordinate points indicating a road configuration or shape to calculate a radius of a circle which passes through these coordinate points and a radius of curvature of a subject road curve. The presence and absence of the curve is determined based on the calculated radius of curvature. The system informs a vehicle driver by a visual display or vocal announcement of the position (point) of the curve together with its radius of curvature or length of the curve as well as an angle of curving.
A memory device such as CD-ROMs or the like which store the road map data and the like has a limited memory or storage capacity. Therefore, the memory device is incapable of storing a plenty of data of coordinate points indicative of road configuration to the extent sufficient to determine curves accurately. Thus, it is likely that the curve is determined only roughly or erroneously.